A plow of the type used to remove snow from a roadway includes a blade which rolls the snow upwardly and then moves it transversely across the face of the blade. To accomplish this, the plow includes a moldboard having a curvilinear configuration which terminates in a lower plowing edge or a scraper blade. The scraper blade usually extends in a forward direction and, in effect, digs into the snow and forces the snow onto the curvilinear moldboard. The contour of the moldboard imports a rolling action to the upwardly moving snow and forces the snow transversely across the face of the moldboard and to the side of the plow.
Over the years, many different moldboard configurations of various curvilinear shapes have been experimented with to arrive at a shape which would insure smooth rolling and transverse movement of wet and powdery snow across the moldboard face. A curvilinear configuration, essentially arcuate in shape and extending in only one planar direction has proven an acceptable, widely used geometrical configuration for the moldboard.
A typical snowplow construction is to roll a mild steel carbon plate, typically of about 1/8, into an arcuate shape to form the moldboard. The framework, typically constructed from structural angle members, is then welded to the rear side of the moldboard to support and prevent the moldboard from fracturing when being hit by rock and other debris from the roadway while also providing a structure for the attachments necessary to operate the plow. Typical examples of such construction may be found by reference to U.S. Pat. No. 3,432,947 to Peitl and U.S. Pat. No. 3,465,456 to Meyer assigned to the current assignee.
From a consideration of plow weight, a steel moldboard is undesirable. It obviously places greater force requirements on the vehicle to which it is attached, and perhaps more importantly requires heavier plow attachments and larger lifting systems than what otherwise may be possible.
From an efficiency consideration, a number of attempts have been made to improve the efficiency of the steel moldboard in plows of the aforesaid type so as to better enhance the rolling motion and transverse movement of the snow across the face of the moldboard. Many of the approaches fundamentally involve a lowering of the coefficient of friction at the surface of the moldboard. For example, wax has long been used by snowplow operators on the moldboard. Moldboards have also been permanently coated with various substances. However, such coatings eventually fail when struck by rocks, stones and other debris from the roadway which impact the moldboard under significant forces.
A number of various materials having extremely low coefficients of friction exist in the art. In particular, ultra high molecular weight polyethylenes have been developed and applied in industrial application where sliding contact is encountered, such as, for example, in wear strips, slide plates, bearings and bushings. Until recently, considerations relating to the mechanical properties of such materials have ruled out the suitability of such materials for use as a moldboard in a snowplow application.
On the basis of weight and cost considerations alone, various types of plastics, other than ultra high molecular weight polyethylene, have been used as moldboards in snowplows. The plastic is preformed into the desired curvilinear shape and applied flush against the frame where it is drilled and fastened in place in the same manner that the steel moldboard is conventionally applied to the frame. Depending upon the properties of the plastic and its durability, plastic moldboards have met with limited success.
The snow plow art was significantly advanced when a high molecular weight, polyethylene material was used as a moldboard to produce a durable, lightweight and significantly improved snowplow as disclosed in U.S. Pat. No. 4,803,790 (and its parent U.S. Pat. No. 4,845,866) to Ciula incorporated herein by reference. The plow disclosed in the '790 patent comprises a conventional frame which includes top and bottom longitudinally extending mounting members approximately equal to the length of the plow blade and a plurality of vertically extending, transversely spaced brace members. Each brace member is secured at one end to the top mounting member and at its opposite end to the bottom mounting member and has inwardly curved, forward edge surfaces extending between the top and bottom mounting members. A generally rectangular and inwardly curved polyethylene moldboard of high molecular weight is attached by threaded fasteners to the top and bottom mounting members in a somewhat flexed or prestressed manner. The rearward surface of the attached moldboard is spaced away from the forward edge surface of the brace members a fixed distance to define a gap therebetween. This gap distance is normally sufficient to prevent contact therebetween during operation of the plow while permitting brace contact during excessive debris impact. More particularly, the moldboard resiliently flexes into and out of the gap during heavy or wet snow removal and this flexing enhances the transverse and rolling movement of the snow over the face of the moldboard. Yet the frame/moldboard mounting arrangement provides brace support for the moldboard when the moldboard is impacted with heavy debris to prevent moldboard fracture. For these reasons, the '807 patent is a significant advance in the art.
This arrangement was improved upon in U.S. Pat. No. 5,088,215 to Ciula, also incorporated herein by reference. In the '215 patent, the high molecular weight, polyethylene moldboard was molded with a desired curvature and the top and bottom molding mounting members changed to allow the moldboard to be snapped into or onto the frame and secured by fasteners in a conventional manner. While the '215 patent improved the frame mounting arrangement, the gap between the moldboard and the brace members is maintained so that the moldboard retains its enhanced snow removal characteristics.
In summary, both designs have achieved considerable success not only because of weight reduction and cost considerations, but also because of the enhanced operation of the moldboard attributed to the characteristics of the polyethylene material and the utilization of the material's ability to spring or flex into the gap designed mounting arrangement.
Snow plows are typically used in hostile environments and are subjected to cold temperatures, moisture, freezing rain, ice, salt, and severe impacts against fixed protrusions such as curbs and from rocks and debris from the roadway. During continued or protracted operation of the plow, debris from the road can lodge itself into the gaps between the moldboard and brace members. If the operator does not take time to periodically clean the gaps, they can become eventually full with solid debris with the result that the resilient mounting of the moldboard onto the frame, provided by the gap, is lost or diminished. More significantly, plow operating temperatures encompass such a wide temperature range, that water collected in the gap can freeze into ice or create ice pockets in the gap. In such instances the gap designed into the moldboard/frame mounting arrangement is lost or drastically reduced. While the moldboard still has superior snow removal characteristics attributed to its low co-efficient of friction, the enhanced ability of the moldboard to transversely move and roll the snow across the face of the plow is diminished.